To provide focused vision, an eye must be capable of focusing light on the retina. The ability of an eye to focus light on the retina depends to a large extent on the shape of the eyeball. If an eyeball is too long relative to the focal length on the visual axis of the eye, an image of a distant object will form in front of the retina, a condition that is called myopia. As a consequence, such an eye, which is called myopic eye, will have difficulties of focusing distant objects on the retina.
Usually, glasses with diverging lenses to enlarge the focal length, so that the image of a distant object will form on the retina, are used for correcting myopia.
In many East Asian countries myopia has reached epidemic proportions, with some large urban centers reporting close to 100% incidence of myopia among 18 to 19 year olds (Jung S.-K. et al., Prevalence of myopia and its association with the body stature and educational level in 19-year-old male conscripts in Seoul, South Korea,” Invest. Ophthalmol. Vis. Sci. 2012, 53, pp. 5579 to 5583). It has been estimated that there have been around 2 billion myopes worldwide in 2010 and some of the recent epidemiological modeling suggests that this number will increase to 5 billion by 2050 (Holden B. A. et al., “Global Prevalence of Myopia and High Myopia and Temporal Trends from 2000 through 2050,” Ophthalmology, May 2016, 123(5), pp. 1036 to 1042). Furthermore, there is an increasing trend for juveniles to develop high myopia (defined as SER≤−5.00 D, where SER stands for spherical equivalent refraction), which substantially increases the risk of eye diseases like cataract, glaucoma, retinal detachment, and myopic maculopathy, all of which can cause irreversible vision loss (Wong T. Y. et al., “Epidemiology and disease burden of pathologic myopia and myopic choroidal neovascularization: an evidence-based systematic review,” Am J Ophthalmol. 2014, 157, pp 9-25). Epidemiological models predict a global increase of high myopia from around 300 million in 2010 to 1 billion by 2050 (See, Holden B. A. et al.). This will inevitably lead to a very high cost to society for treating visual impairment and lost productivity.
Bi-focal and progressive lenses have been trialled clinically with the aim of reducing accommodative lag during near vision tasks which is thought to be one of the main causes of juvenile myopia progression that usually coincides with the beginning of schooling. Some of these trials have shown no effect (e.g., Edwards M. H. et al., “The Hong Kong progressive lens myopia control study: study design and main findings,” Invest. Ophthalmol. Vis. Sci. 2002, 43, pp. 2852 to 2858), while others have indicated a significant retardation of myopia in the first year with saturation in longer term trials (e.g., Gwiazda J et al., “A randomized clinical trial of progressive addition lenses versus single vision lenses on the progression of myopia in children,” Invest. Ophthalmol. Vis. Sci. 2003, 44, pp. 1492 to 1500, Hasebe S. et al., “Myopia control with positively aspherized progressive addition lenses: a 2-year, multicenter randomized, controlled trial,” Invest. Ophthalmol. Vis. Sci. 2014, 55, pp. 7177 to 7188). The saturation issue may be due to some sort of adaptation of visual behaviour to avoid using the addition power or the adaptation of the accommodative system to the presence of the addition power, which leads to the relaxation of the accommodative effort. There is a need to improve progressive-addition lens (PAL) designs to provide a more effective reduction of the accommodative lag and possibly help overcome the saturation of their efficacy to control progression of myopia.
A progressive spectacle lens is usually formed by providing a semi-finished piece of preformed material for the making of a lens, i.e., a semi-finished lens blank. The semi-finished lens blank has a finished lens surface with a specific surface curvature on the front or the back surface and with the other surface not being finished yet. On the surface not finished yet, a free-form surface is formed. In this context, the term “free-form surface” means a surface that may be constructed by the use of piecewise-defined functions such as, e.g., splines and typically shows no point symmetry or axial symmetry. By forming the free-form surface, the progressive spectacle lens is provided with an upper viewing zone, i.e., a portion having a first refractive power for distance vision, a lower viewing zone, i.e., a portion having a second refractive power for near vision, and a corridor, i.e., a portion of providing clear vision for ranges of refractive power between the first and the second refractive power. However, it is also conceivable that a raw element, i.e., an element without any finished lens surface is used for forming the progressive spectacle lens. Throughout the present specification, the term “lens blank” shall encompass the semi-finished lens blank as well as the raw lens.
U.S. Pat. No. 8,162,477 B2 discloses a progressive ophthalmic spectacle lens for myopia correction. This progressive ophthalmic spectacle lens comprises an upper area in which the correction is adapted for peripheral vision of the wearer.
EP 2 069 854 B1 describes a progressive ophthalmic spectacle lens in which the mean addition power throughout the peripheral region is positive and at all radial extents greater that 20 mm from the geometric center of the progressive ophthalmic spectacle lens, is in the range of 0.50 D to 3.00 D.
EP 1 034 453 B1 describes a progressive ophthalmic spectacle lens with a length of the intermediate corridor of 15 mm or less.
U.S. Pat. No. 8,807,747 B2 describes a spectacle eyeglass of the progressive addition type having been designed for myopic children. To this purpose, an ergorama has been constructed, taking into account vision conditions encountered by the children in their everyday life. In particular, the eyeglass has a limited optical power increase between two reference eye directions, a start of the optical power increase which is located quite low in the eyeglass, and an offset value for a meridian line which is higher than that of eyeglasses designed for adults.
U.S. Pat. No. 8,833,936 B2 describes a progressive spectacle lens including an upper viewing zone, a lower viewing zone, a corridor, and a peripheral region disposed on each side of the lower viewing zone. The upper viewing zone includes a distance reference point and a fitting cross, and provides a first refractive power for distance vision. The lower viewing zone, which is for near vision, provides an addition power relative to the first refractive power. The corridor connects the upper and lower zones and provides a refractive power varying from that of the upper viewing zone to that of the lower viewing zone. Each peripheral region includes a zone of positive power relative to the addition power which provides therein a positive refractive power relative to the refractive power of the lower viewing zone. The zones of relative positive power are disposed immediately adjacent to the lower viewing zone, such that the lower viewing zone interposes the zones of relative positive power.
Most of the conventional progressive spectacle lenses currently on the market try to ensure a fairly wide near vision zone with a smooth distribution (smooth gradients) of mean addition power in the lower portion of the spectacle lens, minimizing the size and depth of the peripheral power depressions on both sides of the near vision zone.
WO 97/26579 A1 describes a method of defining a composite progressive power surface by a superposition of a soft and a hard design. WO 97/26579 A1 shows hard designs and a composite design with areas in the distance viewing zone, the left peripheral zone and the right peripheral zone in which the mean power does not exceed 0.130 D.
WO 2011/054058 A1 describes a progressive ophthalmic spectacle lens for correcting myopia. The progressive ophthalmic spectacle lens includes peripheral zones in which peaks with a mean addition power higher than the addition power at the near reference point are located immediately adjacent to the near portion of the progressive ophthalmic spectacle lens. These peaks are laterally separated by at least 20 mm. Further out, the mean addition power may drop steeply to very low values and may even become negative.